Thermostatic switch



July 12, 1955 A. J. KERCHER THERMOSTTIC SWITCH Filed March lO, 1952 INVENTOR. r//wr J /de/ch er BY Mdm 4 TTQRA/E YS THERMSTATIC SWITCH Arthur ll. Kercher, Ecrire-ley, Calif., assigner of one-half to William Wesley Hicks, San Francisco, Calif.

Application March 10, 1952, Serial No. 275,782 lll Claims. (Cl. 2041-137) This invention relates generally to electrical contacting devices such as are employed for the purpose of controlling various electrical circuits. The invention applies particularly when it is desired to secure a rapid opening and closing movement of electrical contacts in response to relatively small operating movements as, for example, where contacts are being opened and closed in response to forces applied from the thermostatic element.

It is an object of this invention to provide a simplified apparatus of the character described, which is particularly adapted to be used with the operation of three-phase power systems and which will aiord the desired positive rapid movement of electrical contacts between open and closed positions without the use of auxiliary relays or contactors. Heretofore the conventional practice has been to use a single-pole thermostat which energizes the solenoid coil of a relay or contactor in order to close or open three poles of a three-phase circuit that carries a substantial current or power load. This generally requires, in addition to the thermostat, a transformer to step down the voltage supply to the thermostat and a relay or contactor which is both expensive and requires frequent maintenance. My device eliminates this auxiliary equipment, and the thermostat controls the three-phase power supply directly.

Another object of the invention is to provide an improved manner for mounting the multiple contacts of such electrical contacting Idevices to attain equal Contact pressure on all points simultaneously without the necessity of permanent magnets or other auxiliary devices.

Additional objects of the invention will appear from the following description in which the preferred embodiment of the invention has been set forth in detail in conjunction with the accompanying drawings.

Referring to the drawings:

Figure l represents a front plan view of a device incorporating my invention illustrating the position of the contacts for the three lines; I

Figure 2 is a cross sectional view taken along the line 2 2 of Figure 1;

Figure 3 is a cross sectional view taken along the line 3-3 of Figure 2;

Figure 4 is an exploded view of the elements illustrated in Figure 2; and

Figure 5 is a fragmentary cross sectional view taken along the line 5 5 of Figure 2.

The apparatus illustrated in the drawings is in the form of a thermostatic switch which is operated in accordance with temperature changes. The operating parts are carried by a mounting plate and include the thermostatic element A and the contacting device B.

One or' the principal parts of the contacting device B is the strip 1l which is formed of suitable spring metal, such as hardened spring steel or phosphor bronze. One end portion 11a of the strip is anchored to the fixed support l@ by an adjustable means which will be more fully hereinafter described. An adjacent portion 11b is formed as an integral loop thus affording an interposed resilient nted States Patent Oce 2,7l399 Patented July 12, 1955 portion. The free end portion 11C can move in opposite directions and is operatively connected to the electrical contact elements. That portion of the strip intermediate the free end 11e and the loop portion 11b is cut away to form an integral tongue 12. The free end of the tongue 12 is bevelled to form a knife edge which normally engages a lixed abutment 13. The portion 11d of the strip which lies between the free end of the tongue 12 and the loop portion 11b is adapted to receive operating forces from the thermostatic device A.

The anchoring of the strip portion 11a to the xed support 10 is such that the loop portion 11b is normally stressed in predetermined amount within its elastic limit. This makes possible a snap action ofthe strip.

The portion 11a is provided with an orice which accommodates a stud 1.6 by which the same is secured to the threaded pad 17 on the backing plate itl.

The end 11C is also provided with a slot 18 which is adapted to accommodate a grooved stud 19 mounted on the back of a contact carrier plate 21. The Contact carrier plate 2l. is illustrated particularly in Figure 4 and is formed of a pair or" non-conductive discs 22 and 23 which are held together by the stud 19. The stud .19 is provided with a cylindrical bore 2li and is slidably mounted upon a pin 26 retained in position by the cover plate 27. The contact carrier plate 2l is free to slide along the pin 26 under the urging ot' the metallic strip ll.

The backing plate 1G also carries a pin 31 which is adapted to be accommodated by an orifice 32 in the contact carrier plate 2l. lt will be noted that the pins 26 and 31 are parallel and that the contact carrier plate 21 is also free to ride longitudinally along the pin 31. The purpose of the pin 31 is to prevent rotation ofthe member 21 about the pin 26.

The member 2l carries three sets of contactors 33, 34 and 36 which are secured to the member 21 by pins 37. They are preferably loosely mounted for rocking movement about the axis formed by the pins 37 and it will be noted they are slightly arcuately shaped so such rocking movement may be had.

The cover plate 27 is also made of non-conductive material and forms a base for three sets of contact assemblies 43, i4 and 46 whose contacts 43a and b, 44a and b and b are adapted to be engaged by the contactors 33, 34 and 36 respectively on the contact carrier plate 21. When the contact carrying plate 21 is in the position illustrated in Figures 2 and 5, a circuit will be completed between the contacts 43a and 4319, the contacts 44a and 44h and the contacts 46a and 461). in this manner three line operation is secured.

The thermostatic means incorporated in the structure consists of a metal tube 4S one end of which is secured to the mounting lil. Within this tube there is a rod 49 one end of which is attached to the free end of the tube 43 in any suitable manner and the other end of which has a threaded engagement with which, in turn, carries a pointer 52. To form an operative engagement between the rod and the resilient strip 11 the strip il is apertured to receive the rod 49 and is provided with a bushing 54. The upper face of the bushing 5d is spherically shaped to form a concave seat for engaging the adjacent spherically shaped end portion of the member 5l. The tube 4S and the rod 49 are formed of different metals having different thermal coeicients of expansion. Assume, for example, that the tube 48 is immersed in water or in liuid medium being heated, an increase in temperature will cause elongation of the tube with the result that the rod 49 will transmit motion to the resilient strip 1l to llex the strip to the left, as viewed in Figure 2. A decrease in temperature, on the other hand, will cause contraction of the tube release the pressure on with the result that the rod 49 will f: u., the resilient strip 11 and the same will snap to the position illustrated in Figure 2.

A simple temperature scale has been provided upon the cover plate 27 so that one may manually set the device for different temperature levels of operation. it will be apparent that the threaded engagement 'oc-tween the member 51 and the rod 49 varies the relative positioning of the rod 49 with respect to the resilient strip as the pointer 52 is manually rotated.

Operation of the device may briey be described as follows:

It will be presumed that the device is set for a given temperature level of operation and that the contacts 43a, 44a and 46a (the line terminals) are connected in suitable circuits for supplying current. It will be assumed that the contacts 5.1311, Mb and 6b (the load terminals) are connected to a heating element. This heating element heats the fluid, such as water, in which the thermal contact tube 48 is immersed. Assuming that the temperature of the tube is is above the temperature level for which the device is set, the resilient spring strip lll will occupy a position in which the contactors 33, 34. and 36 will not engage the assemblies 43, d4 and 46 but will be in a position, not shown, to the left, as illustrated in Figure 2. The free end of the tongue Vl?. will be slightly above the plane of the adjacent portions of the resilient strip 11. Also, the free end of the resilient strip 1l will be in a position, to the left, as illustrated in Figure 2. As the temperature of the tube 4S reaches approximately the temperature level of operation, the spring strip .ll will be permitted to flex until it passes dead center position. Dead center position corresponds to that position of the tongue 12 in which it is in the same plane as the adjacent portions of the resilient strip 1li. The free end of the spring strip then snaps to the right, as viewed in Figure 4, to rapidly bring the contactors 33, and 3o into engagement with the members 43, 44 and lo respectively closing the three circuits to the heating element. The tripod arrangement of the contacts on member 2l makes it certain that the pairs of contacts 33, 34 and 3l? will close with equal pressure on 43, 44 and 46 so as to ensure that all three lines will be closed simultaneously. Assuming that the fluid in thermal contact with the tube 4.15 is being heated by current ow in the electric heating element, when a predetermined elevated temperature is reached, the rod a9 and the resilient spring strip ll are drawn to the left (Figure 2) to such an extent as to snap the spring ll past dead center position. Thereupon the contactors 33, 34- and 36 will be disengaged from contacts @3a and b, 44a b and 46a and b and the three circuits will be opened. The lost motion connection between the free end of the resilient spring strip and the remainder of the device is such that the contacts are not moved toward open position until after the resilient spring ll has been flexed sufficiently far to secure the desired snap ac lon, that is, past its dead center position.

lt will be apparent from the foregoing that l have provided a thermostatic snap action switch suitable for three line operation. The lioating disc 2l will exert equal pressure upon the contacts 43a and b, 44a and b, and 46a and b. The snap action is quick and smooth and prevents arcing. The somewhat ilexible mounting of the contacting strips 33, 34 and 36 will further serve to equalize the pressure exerted by the members 33, 34 and 36 upon their respective contacts. The pins 26 and 31 serve to keep the disc 2l in alignment at all times, thereby insuring simultaneous closing of the three circuits.

I claim:

l. In an electrical contacting apparatus particularly adapted for use in connection with controlling three circuits, a at strip of spring metal, the strip being provided with a resilient portion near one end of the same, means serving to anchor said one end of the strip to a xed support whereby the other end of the strip is free for llc the pairs of contactsY movement in opposite directions in a circumferential path, spring tension means intermediate the ends of said strip to alford snap action for the strip, a disk mounted upon the free end of said strip and adapted to be moved thereby, a pair of fixed pins passing through said disk and adapted to maintain the same in predetermined alignment, three contactors on said disk, and three sets of contacts on said fixed support adapted to be engaged by said contactors.

2. In a snap acting thermostatically controlled switch adapted for use in connection with controlling a three line circuit, means for supplying equal pressure to three sets of contacts comprising a disk provided with three contactors movable into and out of engagement with said sets of contacts, means for moving said disk and said contactors in a circumferential path in and out of engagement with said contacts comprising a resilient strip which is stressed within its elastic limit to allord snap action and subject to a thermally controlled element, and a pivotal connection between said strip and the contactorcarrying disk.

3. In a snap acting thermostatically controlled switch adapted for use in connection with controlling a three line circuit, means for supplying equal pressure to three sets of contacts comprising a disk provided with three contactors, means for moving said contactors in a circumferential path in and out of engagement with said contacts comprising a snap acting resilient strip subject to a thermally controlled element, a pivotal connection between said strip and said contactor-carrying disk and a pair of xed parallel pins permitting movement of said contactorcarrying disk in a plane dened by the longitudinal axis of said pins and preventing rotation of said contactorcarrying disk about the axis of either of said pins.

4. ln a snap acting thermostatically controlled switch adapted for use in connection with controlling a three line circuit, a base plate, a cover plate spaced from said base plate, three sets of contacts mounted on said cover plate, a disk disposed between said plate, three contactors loosely mounted on said disk, and means for supporting and moving said contactors simultaneously in a circumferential path in and out of engagement with said contacts, said means being responsive to a thermally controlled element.

5. A device as in claim 4 together with means for preventing rotation of said disk and at the same time permitting movement of said disk to allow said contactors to move into and out of engagement with said contacts.

6. In a snap acting thermostatically controlled switch adapted for use in connection with controlling a three line circuit, a base plate, a cover plate spaced from said base plate, three sets of contacts mounted on said cover plate, a disk disposed between said plates, three arcuately shaped contactors loosely mounted near the outer periphery of said disk to permit the contactors to rock about the lateral axis of said contactor, and means for supporting and moving said contactors simultaneously in a circumferential path in and out of engagement with said contacts, said means being responsive to a thermally controlled element.

7. A device as in claim 6 together with means for preventing rotation of said disk and at the same time permitting movement ol said disk along a circumferential path.

8. A device as in claim 6 together with means for preventing rotation of said disk and at the same time permitting movement of said disk along a circumferential path comprising a vertical pin on said base plate, a vertical pin on said cover plate, and a pair of oriliees in said disk to allow a movement of said disk along a circumferential path and in a plane dened by the longitudinal axis of said pins.

9. A device as in claim 8 in which the mounting means for each of said contactors consists of a pair of pins disposed along the lateral axis of each of said contactors.

l0. ln a snap acting thermostatically controlled switch adapted for use in connection with controlling a three line circuit, a base plate, a cover plate spaced from said base plate, a at strip of spring metal disposed between said plates, thermally controlled means having one portion of said element connected to said base and having the other portion of said element connected to said at strip, means serving to anchor one end of the strip to a fixed support whereby the other end of the strip is free to move in opposite directions in a circumferential path, a disk disposed between said plate and pivotally mounted on the free end of said at spring, three sets of contacts mounted on said cover plate, three arcuately shaped contactors loosely mounted near the outer periphery of said References Cited in the iile of this patent UNTED STATES PATENTS 2,071,149 Wilms et al. Feb. 16, 1937 2,092,478 Sommermeyer Sept. 7, 1937 2,190,402 Curzon Feb. 13, 1940 2,314,989 Kercher Mar. 30, 1943 

